JPH0269760A - Layer formation method for electrophotographic photoreceptor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to electrophotographic copying machines, laser beam printers, etc.
Regarding the manufacturing method of electrophotographic photoreceptors used in the electrophotographic application field such as CRT grille/tar, more specifically, in the dip coating method when manufacturing electrophotographic photoreceptors, a film is formed between the top and bottom of the electrophotographic photoreceptor due to liquid dripping. This invention relates to a coating method that does not cause thickness differences.

[Conventional technology]

In recent years, various organic photoconductive materials have been developed as photoconductive materials for use in electrophotographic photoreceptors, and in particular, functionally separated electrophotographic photoreceptors in which a charge generation layer and a charge transport layer are laminated have already been put into practical use, and are used in copying machines. and installed in printers.

A dip coating method is generally known as a method for manufacturing electrophotographic photoreceptors, and while this dip coating method is simple and excellent in mass production, it is also known to cause a film thickness gradient from the start of coating to the end point. .

That is, when dip coating is carried out at a constant speed, due to liquid dripping, the film thickness tends to be thinner near the start of coating, ie, at the top, than at the end of coating, ie, at the bottom.

Although the degree of this problem varies depending on the viscosity, solid content, and fluidity of the liquid, it becomes a hindrance in electrophotographic photoreceptors where it is necessary to obtain a uniform film thickness. This is particularly noticeable when using a low concentration coating liquid. In a laminated electrophotographic photoreceptor, the charge generation layer coating liquid generally has a strong tendency toward this. In order to avoid this liquid dripping, methods such as continuously changing the dip coating speed or adding a large amount of low-boiling point solvent to promote dryness to the touch are taken, but the uniformity of the film thickness is insufficient. there were.

[Problem to be solved by the invention]

In particular, the length of the electrophotographic photoreceptor itself is limited in copying machines and laser beam printers that aim to be smaller and lighter in recent years, so it is necessary to provide a photosensitive layer with a uniform thickness over the entire length of the conductive substrate. Therefore, uniformity of film thickness in dip coating remains a major issue.

The present invention relates to a method for manufacturing an electrophotographic photoreceptor that satisfies the above requirements, that is, has a uniform film thickness from the upper end to the lower end of the coating.

That is, an object of the present invention is to eliminate vertical differences in coating film thickness in an electrophotographic photoreceptor manufactured by a dip coating method, thereby producing an electrophotographic photoreceptor without sensitivity differences and image density unevenness due to differences in film thickness. That's true.

[Failure to solve the problem]

As a result of various studies to overcome the problem of liquid dripping in dip coating, we have been able to prevent dripping V by controlling the fluidity, or rheology, of the electrophotographic photoreceptor coating liquid, resulting in a uniform film. It has been found that an electrophotographic photoreceptor can be produced which has a large thickness, thereby causing no unevenness in sensitivity or unevenness in image density.

That is, the present invention provides a method for forming a photosensitive layer of an electrophotographic photoreceptor by a dip coating method, in which the average particle size is 0.05 to 0.
It is characterized by using a coating liquid which contains 1.0 to 3.0 weight 2 of a charge generating material of 1 μm based on solid content and exhibits non-diffusion flow excitability.

The present invention will be described in detail. It is generally known that liquid dripping in dip coating becomes more pronounced as the concentration and solid content of the coating liquid decreases. Considering the case where a laminated electrophotographic photoreceptor is manufactured by the dip coating method, the optimum film thickness of the charge generation layer is 0.1 to 2.0μ, so when used with a coating solution of low concentration and low solid content. It is also known that when a film thickness difference occurs in the charge generation layer due to liquid dripping, a sensitivity difference corresponding to the difference and an accompanying difference in image density occur. The charge generation layer coating liquid is used by dispersing the charge generation material in a resin binder and adjusting the concentration and solid content as appropriate.
Unlike simple resin solutions, they have non-nietonic flow and often thixotropic properties. When dip coating is performed using a coating solution with very strong chicken tropism, the shear force generated between the coating solution and the substrate is small or absent at the top of the coating, resulting in a coating solution with a high apparent viscosity adhering. As the coating progresses, the apparent viscosity decreases due to shear force, and the film thickness distribution tends to be thicker at the top and thinner toward the bottom.

On the other hand, when a coating liquid with weak thixotropy is used, the flow becomes close to Newtonian, so liquid drips, and the coating liquid tends to be thin at the top and thicken downward.

In the present invention, this non-neeton fluidity is artificially imparted to the coating solution, and it is possible to obtain a uniform film thickness by balancing both the adhesion of the coating solution due to thixotropy and the spreadability due to liquid dripping. I made it.

That is, when dispersing the charge generating material in a resin binder solution, the particle size of the charge generating material is adjusted to 0.05 to 0.10μ (
Average particle size/particle size distribution analyzer CAPA-70 manufactured by Aiba Seisakusho
It has been shown that a uniform film thickness can be obtained using the dip coating method by using a coating solution that is stabilized within the range of 0% (measured at 0%) and has a solids content of 1.0% to 3.0% during coating. I found it. Although there is no numerical index for chickentropy, a charge generating layer coating solution having an average particle size and solids content within the above range exhibits appropriate chickentropy. In addition, depending on the type of charge-generating material, resin binder, and solvent used, there may be a certain degree of difference in thixotropy, making it inappropriate to obtain a uniform film thickness. Optimal chicken tropism can be obtained by adjusting the dispersion and/or solids content within the range of average particle size and solids content.

Furthermore, it is necessary to keep the above average particle size and solid content constant from the start to the end of application, and if the average particle size becomes smaller (if the particles become more dispersed), chicken tropism will occur. It becomes stronger and the amount of coating liquid attached increases.
Further, when the average particle size increases (when particle aggregation progresses), the thixotropy becomes weaker and the amount of coating liquid attached decreases. It is clear that as the solid content increases, the amount of coating liquid adhered increases, and as the solid content decreases, the amount of adhered liquid decreases. In either case, the film thickness is uneven, which deviates from the purpose of the coating method for obtaining a uniform film thickness, which is the objective of the present invention.

When producing an electrophotographic photoreceptor according to the present invention, the substrate itself is conductive, such as aluminum, aluminum alloy, copper, zinc, stainless steel, pananoum, molybdenum, chromium, titanium, nickel, indium, gold. In addition, plastics (for example, polyethylene, polypropylene, polyethylene, (vinyl chloride, polyethylene terephthalate, acrylic resin, polyethylene fluoride, etc.), and conductive particles (for example, metal particles such as copper, aluminum, etc., particles of caden black, tin oxide, antimony oxide, titanium oxide, etc.) can be used. A substrate (with a conductive layer) coated on a plastic with a suitable binder (e.g. urethane resin, epoxy resin, phenoxy resin, phenol resin, polyvinyl alcohol, acrylic resin, polyamide, etc.), conductive particles A substrate impregnated with glass or paper or conductive?
A glass stick having a reamer or the like can be used.

An intermediate layer having gearing and adhesive functions can also be provided between the conductive substrate and the photosensitive layer.

Intermediate 11 is made of casei/, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer polyvinyl butyral, phenolic resin, polyamide (nylon 6
, nylon 66, nylon 610, copolymerized nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin, aluminum oxide, etc.

The thickness of the intermediate layer is 0.1 micron to 10 micron, preferably 0.3 micron to 3 micron.

A charge generation layer containing one charge generation material is formed on the conductive substrate or on the above-mentioned intermediate layer. As charge generating materials, selenium-tellurium, biryllium dyes, thiopyrylium dyes, phthalocyanine pigments, aftanthrone pigments,
Nope/zupyrenequinone pigments, pyranthrone pigments, trisazo pigments, nosazo pigments, azo pigments, indigo pigments, quinacrine pigments, asymmetric quinocyanine, quinocyanine, and the like can be used.

The charge generation layer is prepared by thoroughly dispersing the above charge generation material together with 0.3 to 4 times the amount of binder resin and a solvent using a method such as a homogenizer, ultrasonic wave, ball mill, vibrating sol mill, sand mill, or attritor roll mill. , coating-drying and forming. Its thickness is about 0.1 to 2.0 microns.

Binders that can be used when forming the charge generation layer by coating include polyvinyl butyral, polyarylate (condensation polymer of bisphenol A and phthalic acid, etc.),
Insulating resins include polycarbonate, polyester, phenoxy resin, polyvinyl acetate, acrylic resin, PolyJ acrylamide resin, polyamide, polyvinylpyridine, cellulose resin, urethane resin, epoxy resin, casein, polyvinyl alcohol, and polyvinylpyrrolidone.

Solvents that dissolve these resins vary depending on the type of resin. Specifically, examples of solvents include methanol, ethanol, and Inglono! Alcohols such as alcohol; acetone,
Ketones such as methyl ethyl ketone and cyclohexanone:
Amides such as N,N-trimethylformamide and N,N-trimethylacetamide; Sulfoxides such as dimethyl sulfoxide; Ethers such as tetrahydrofuran, dioxane, and ethylene glycol monomethyl ether;
Esters such as methyl acetate and ethyl acetate; aliphatic halodanated hydrocarbons such as chloroform, methylene chloride, dichloroethylene, carbon tetrachloride, trichloroethylene, benzene, toluene, xylene, monochlorobenzene, dichlorobenzene, etc. aromatics, etc. can be used.

A charge transport layer containing a charge transport material can be formed by selecting an appropriate binder. Examples of resins useful as binders include acrylic resin, polyarylate, polyester, polycargonate, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer, polyvinyl butyral, polyvinyl formal, polysulfone, polyacrylamide, polyamide, and chlorine. Insulating resin such as carbonized rubber, or poIJ+N-vinylcarbazole,
Organic photoconductivity such as polyvinylanthracene and polyvinylpyrene? Rimmer can be mentioned.

The charge transport material is selected from hydrazone compounds, stilbene compounds, carbazole compounds, pyrazoline compounds, oxazole compounds, thiazole compounds, triarylmethane compounds, I-aryl alkanes, and the like. The charge transport layer can be provided by dissolving the above-mentioned binder and charge transport material in a solvent and applying the solution.

Since the charge transport layer has a limit in transporting charge carriers,
It is not possible to make the film thicker than necessary. - For boat fishing, the range is 5 microns to 50 microns, with a preferred range of 8 microns to 35 microns.

Hereinafter, the present invention will be explained by examples. In the following description, all parts are by weight.

Examples 1 to 7, Comparative Examples 1 to 7 An aluminum cylinder with a diameter of 3 ON and a length of 260 fl was prepared as a base.

On the other hand, 100 parts of conductive powder obtained by coating titanium oxide with tin oxide containing 10% antimony oxide in an amount of 75 parts %, 100 parts of resol type phenolic resin, 30 parts of methanol and methyl cellosolve were added. In addition to a solution consisting of 100 parts, ? - It was well dispersed using a Lumil device and made into a paint. This coating material was dip-coated onto the substrate and cured by heating at 140° C. for 30 minutes to form a 20 μm thick conductive undercoat layer.

Polyamide resin (6-66-61
0-12 quaternary nylon copolymer) and 3 parts of 8-nylon resin (methoxymethylated 6-nylon, methoxylation rate 30%) were dissolved in a solvent consisting of 50 parts of methanol and 40 parts of butanol, and coated. Apply the liquid by dipping to 0.5
An intermediate layer of μ thickness was provided.

Next, 1 part of the polyvinyl penzole resin represented by the structural formula and 50 parts of cyclohexanone were dispersed in a sand mill device with 1φ of the median being the lath beads. Dispersion time and diluting solvent (
Coating solutions having various average particle diameters and solid content concentrations were prepared by varying the ik (tetrahydrofuran), and each coating solution was applied to the intermediate layer using the dip coating apparatus shown in Fig. 1. Example 1~
Charge generation layers of Comparative Examples 1 to 7 and Comparative Examples 1 to 7 were formed.

In FIG. 1, a substrate 1 is lowered into a coating liquid pot 3 for dip coating by the operation of a lifting device 2 for dip coating, and then raised to be dip coated. During this dip coating, it is necessary to keep the chicken-tropic property and solids content of the coating liquid constant, and for this purpose, the coating liquid is continuously circulated from the coating liquid reservoir (tank) 4 into the coating liquid bottle 3 by circulation 5. circulate. The circulation rate may be such that it does not cause unevenness on the coated surface, and in the present examples and comparative examples, a circulation rate of 1 to 5 mm per minute was appropriately used.

Next, 10 parts of bisphenol 2 type polycargenate resin (number average molecular weight 22,000) and 9.5 parts of the compound represented by the structural formula were dissolved in 150 parts of monochloropenze and 15 parts of dichloromethane, and this solution was dissolved in Examples 1 to 1.
7 and Comparative Examples 1 to 7, and dried to form a charge transport layer having a thickness of 20 μm.

The electrophotographic photoreceptor thus obtained was incorporated into a Canon FC-5 plain paper copying machine, and actual image evaluation was performed.

Table 1 shows the processing conditions and evaluation results for dip coating the charge generation layer.

1. Thixotropic properties: Viscosity when left standing (standing at room temperature for 1 day or more) and strong shaking (using an experimental shaker, shaking number 300 times/minute x 3 minutes, shaking width 4)
The viscosity was measured using a B-type viscometer (immediately after shaking), and the difference between the values was used as a measure of the strength of cythixotropy.

U/R3...Viscosity when standing still is more than 3 times the viscosity during strong vibration2...1.5 times to 3 times1.
...Less than 1.5 times.

*2 Regarding the difference in film thickness during dip coating, the film thickness of the charge generation layer after coating and drying was measured by replacing it with the density difference using a reflective density needle. The measuring device is Macbeth RD-914.
The mold and the values in the table were calculated using the following formula: Reflection density Dc = Density in the center DL = Reflection density in the area 10 points above the bottom edge of the coating *3 Mount each sample for the difference in the top and bottom of the actual fired halftone image. A halftone image was actually copied using a Canon FC-5 plain paper copying machine, and the image density was measured using a reflection densitometer.

The numerical values in the table were determined using the following formula: Reflection density de at the bottom = Density dt at the center = Reflection density at the area 1011 above the bottom edge of the image (corresponding to the bottom of the photoreceptor) Examples 8 to 12 Comparative Examples 8 to 12 The substrate, conductive layer, and intermediate layer were prepared in the same manner as in Example 1.

Next, 2.5 parts of a disazo pigment represented by the structural formula, basic structure (number average molecular weight so, ooo, butyral value 75, t, m, n
is a positive integer) polyvinyl butyral resin 1
1 part and 50 parts of cyclohexanone were dispersed using a sand mill apparatus using 1φ glass beads as the median. Examples 1-7
Similarly, dispersion time and diluting solvent (methyl ethyl ket) y)
Coating liquids having various average particle sizes and solid contents were prepared by changing Ji, and the charge generation layers of Examples 8 to 12 and Comparative Examples 8 to 12 were formed by dip coating in the same manner as Examples 1 to 7. did. Regarding the coating speed, the average film thickness after drying is 190f.
Coating was carried out at a constant speed so that the coating was applied at a constant speed of f//m''.

Next, 10 parts of bisphenol 2 type polycarbonate resin (number average 22,000) and 9.5 parts of the compound represented by the structural formula were dissolved in 50 parts of monochlorobenzene and 15 parts of dichloromethane, and this solution was dissolved in Examples 8 to 12 above.
It was coated on the charge generation layers of Comparative Examples 8 to 12 and dried to form a charge transport layer with a thickness of 20 μm.

Examples 1 to 7 of the electrophotographic photoreceptors thus obtained
It was evaluated in the same manner.

Table 2 shows the processing conditions and evaluation results for dip coating the charge generation layer.

Examples 13 to 17 Samples completely similar to Example 2 were prepared except that a disazo pigment represented by the structural formula was used. Examples 13 to 17 shown in Table 3 were prepared by varying the dispersion time and the amount of diluting solvent. The evaluation method was exactly the same as in Examples 1 to 12, and the results are also listed in Table 3.

As is clear from the above Examples and Comparative Examples, a coating liquid with thixotropy corresponding to rank 2 in the table, that is, a coating liquid with a viscosity at rest of about 1.5 to 3.0 times the viscosity at strong vibration, is used. The coating liquid shown here exhibits the most preferable non-Newtonian flow when used in dip coating as a charge generation layer coating liquid, and is suitable as a means for coating an electrophotographic photoreceptor with no uneven top and bottom image density. Further, such a coating liquid can be obtained by adjusting the average particle size of the charge generating material to 0.05 .mu.m to 0.1 .mu.m and dispersing and adjusting the solid content of the coating liquid to 1.0% to 3.0%.

[Effects of the Invention] According to the present invention, the difference in coating film thickness and the resulting difference in image density, which have been problems when manufacturing electrophotographic photoreceptors by the dip coating method, can be solved by adjusting the coating solution. can be resolved optimally.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a dip coating apparatus used in carrying out the present invention.

Claims (1)

[Claims] In a method of forming a photosensitive layer of an electrophotographic photoreceptor by a dip coating method, a charge generating material having an average particle size of 0.05 to 0.1 μm is contained in an amount of 1.0 to 3.0% by weight based on the solid content and is non-containing. A method for forming layers on an electrophotographic photoreceptor, characterized by using a coating liquid exhibiting Newtonian fluidity.